1. Field of the Invention
The invention relates to cannulas and more particularly to a specialized cannula construction for aspirating air emboli from blood vessels.
2. The Prior Art
Entrapment of air in the left side of the heart is one of the great hazards of open-heart surgery due to the probability that the entrapped air will enter the systemic circulation. Conventionally, most open-heart surgery is conducted either through a sternal splitting incision with the patient supine or through a right anterolateral sub-mammary incision with the patient's right side elevated approximately 30.degree. from the horizontal. In both of these positions the highest point in the central cardiovascular system is the ascending aortic arch between the aortic valve ring and the innominate artery takeoff.
In many patients, usually those undergoing mitral valve surgery, the physician will work through the left atrium with the heart beating, the aortic valve acting as a dam to maintain an empty left heart. The perfusion pressure keeps the aortic valve closed and minimizes the amount of air which enters the aortic route from the left ventricle. It has been found, however, that even the simplest digital manipulation of the mitral valve may trap air in the left ventricle and, if the ventricle is still beating, the next contraction will expel this air through the aortic valve into the aorta. The air will then collect in the aorta at its highest point. The air, in the form of a bubble is characterized as an air embolus. Under normal circulatory dynamics, aortic flow would certainly sweep such air embolus into the innominate artery and thereby enter the intracranial circulation. The serious adverse effects of this damaging air embolus are well known. If the air embolus is comparatively large and gains access to the right carotid artery, serious neurologic defects in the left half of the patient's body will likely result.
It has been discovered, however, that during the use of a cardiac bypass machine, when the heart is open, there is no return of blood through the vena cava and little or no forward motion of the blood through the aortic valve. Hence, the air embolus, at this point in the surgical procedure, is imprisoned in the aortic arch.
In order to alleviate the serious risk of a disabling air embolus when the heart is returned to normal function, it is known to suture in place a vent in the highest portion of the aortic arch during surgery. See, for example, Groves and Effler, 47 J. Thoracic and Cardiovas. Surg. No. 3, March, 1964, page 349, et. seq.
The mentioned vent structure and related prior art devices are seriously deficient in that they merely provide a communication between the aorta and the exterior of the blood vessel permitting blood and gases to continuously flow out of the vent. The presence of blood flowing from the aorta tends to obscure the surgical field and complicate the physician's work. It is also known to utilize a conventional needle or the like connected to a vacuum which is then penetrated into the aorta in an effort to aspirate the air embolus. Conventional needles have proved to be cumbersome and difficult to use. For example, it has been found extremely difficult to appropriately penetrate the aorta so as to assure that the aspirating tip of the needle is in direct contact with the air embolus. If the needle travels too far through the embolus, only blood will be aspirated. If the needle is adjacent the air embolus, but the aspirating bevel of the needle facing away from the embolus, the embolus will not be aspirated. Furthermore, because the prior art aspirating needle is attached to a suction line, the natural weight of the suction line tends to force the needle out of the vertical penetration position and cause the needle to lie flat against the inside of the aorta. Not only does this position frequently remove the aspirating tip of the needle away from the air embolus, it maximizes the likelihood of inadvertent movement of the needle relative to the aorta risking laceration of the aorta or at least bringing undesirable tissue damage to the blood vessel.
Accordingly, it would be a significant contribution to the art to provide an air embolus aspirating device having maximum surface area in contact with the air embolism for aspiration purposes, which is configurated to lie flat against the aorta or other patient surface during the course of aspiration and which will easily couple with existing vacuum lines and/or fluid delivery circuits for versatile aspiration of air emboli from the blood vessel. Such a device is disclosed and claimed herein.